Neuropro

Summary
Several independent lines of evidence suggest an important role of prolyl oligopeptidase (PREP) in brain function and dysfunction. Aberrant PREP activity is involved in the progression of neurodegenerative disorders and PREP inhibitors have great potential for the treatment of memory and cognition deficits associated with neurodegenerative diseases. NEUROPRO aims to unravel the biological role of PREP and PREP-like proteins in neuropathology, determine the mode of action of PREP inhibitors and firmly establish their therapeutic potential. To achieve this goal, a multidisciplinary approach will be used to study PREP regulated pathways in health and disease, identify physiological PREP substrates, characterize inhibitor targets, develop and validate new drugs, and generate specific cell lines and animal models of neurodegenerative diseases.

Background
PREP is an serine peptidase cleaving carboxyterminal of proline residues in small peptides. The first reports on the pharmacological activity of PREP inhibitors demonstrated their ability to enhance cognitive functions in laboratory animals. In rats with lesions of the nucleus basalis magnocellularis, a PREP inhibitor significantly shortened the escape latency in the Morris water maze as compared to the vehicle-treated group. It also enhanced radial maze performance in hippocampal lesioned rats and significantly prolonged the retention time in rats with middle cerebral artery occlusion in one trial passive avoidance task. Another PREP inhibitor demonstrated its beneficial effects in short-term, long-term, reference and working memory tasks in aged mice, as well as in rodents and monkeys with chemically induced amnesia or spontaneous memory deficits. In addition, PREP inhibitors exert neuroprotective effects in models of neurodegeneration, in vivo and in vitro. PREP inhibitors prevented neuronal damage induced by four-vessel-occlusion transient ischemia in rats. In experiments on primary cultures of cortical neurons or cerebellar granule neurons addition of a PREP inhibitor delayed age-induced apoptosis. PREP is suggested to be involved in cell proliferation and differentiation. In animal studies repeated administration of a PREP inhibitor to partially hepatectomized rats suppressed the rate of liver regeneration and suppressed liver growth. A possible role of PREP in the proliferation and differentiation of the neuronal precursors has not been studied yet. Inhibitors of PREP suppress the generation of ?-amyloid protein in cell lines. The expression of PREP in hippocampus dramatically increases with age and the brains of young APP transgenic Tg2576 mice have higher PREP activity in this brain area. It has been hypothesized that the promnesic and neuroprotective effects of PREP inhibitors are due to the modulation of neuropeptide concentrations, which are known to influence learning and memory. Administration of PREP inhibitors elevated the levels of substance P, thyrotropin-releasing hormone (TRH), and arginine-vasopressin in the cerebral cortex and hippocampus and caused a significant increase in substance P and ?-MSH in the frontal cortex and hypothalamus. Remarkably, PREP is primarily located in the cytosol, while the interactions between peptides and their receptors occur on the cell surface. Subcellular localisation of PREP suggests additional intracellular functions for this enzyme. Recently it was shown that proteolytic activity of PREP is responsible for the regulation of IP3 levels. The reduced PREP activity was found to amplify substance P mediated stimulation of IP3. Furthermore recent findings indicate that PREP is involved in the regulation of peptide/protein secretion and that it may contribute to the hydrolysis of several intracellular peptides such as fragments of haemoglobin, myelin basic protein, PEP19, S-100 calcium binding protein ß, among others. These proteins are known to be involved in a number of important cellular functions

Aim:
The aim of this research is to obtain insight in the role of PREP in peptide metabolism in brain function and dysfunction and to translate this basic research into new therapeutic approaches for neurodegenerative diseases. The three main objectives of the consortium are:

1) to unravel the mode of action of PREP and PREP-like enzymes in health and disease.

2) to develop new drugs.

3) to discover new therapeutic targets.

Expected results:
NEUROPRO expects to gain a better understanding of peptide metabolism under physiological and pathological conditions. In particular, we anticipate novel insight in the role of PREP in the processing and deposition of ?-amyloid and ?-synuclein peptides and the connection with Alzheimer’s and Parkinson’s disease. Furthermore, the studies will shed light on the interaction of PREP with microtubules, its role in the inositol pathway, intracellular transport and secretion. The generation and characterization of cellular and animal models for PREP deficiency will result in the identification of physiological substrates. PREP inhibitors will be studied in detail to establish their specificity and possibly identify off-targets. Novel inhibitors will be developed making use of in silico and structural analysis.

Potential applications:
The outcome of this project is expected to lead to proof of concept that PREP inhibition is a valid therapeutic strategy in the treatment of neurodegenerative diseases. New methods for early detection, prevention or restoration of neurodegenerative diseases will also be explored. Apart from their participation in the research project, the SME's - developing peptide technology, animal models and drug candidates - will be instrumental in translating the results of the consortium into clinical applications and in disseminating these results to pharmaceutical companies.

Duration: 48 months